1. Field of the Invention
The present invention relates to photosensitive polycyclic polymers, compositions thereof, films formed therefrom and processes for the use of such in microelectronic and optoelectronic devices, and more particularly to such polymers, compositions, films and processes where the polymer encompasses repeating units that result from the addition polymerization of functionalized norbornene-type monomers, where such films are characterized by, among other things, low internal stress and high temperature stability.
2. Description of Related Art
The rapid development of the microelectronics and optoelectronics industries has created a great demand for dielectric polymeric materials. At least in part, this demand is driven by these industries' advances toward devices that require such materials to achieve higher functionality and operational speeds than devices made in the past. For example, advanced microelectronic devices such as high density memories and microprocessors generally require several layers of closely spaced electrical interconnects that must be insulated from one another by a dielectric material with the lowest possible dielectric constant to reduce capacitive coupling effects.
While it has been shown that the dielectric constant of silicon dioxide can be reduced (from 3.9) by doping the oxide with fluorine and/or carbon, the reductions obtained are not large and often the resulting films pose reliability problems. Hence the aforementioned demand for dielectric polymeric materials that can provide larger dielectric constant reductions. However, despite the lower dielectric constants such materials offer, finding polymeric materials that are compatible with well established processing methods and that have appropriate mechanical, chemical and thermal properties, for example low internal stress and thermal stability, has been difficult. Despite this difficulty, efforts have continued to find appropriate materials as the potential uses for such polymeric materials has become apparent.
Thus unlike inorganic materials such as doped oxides, it has been found that a polymeric material with an appropriate modulus can enhance the reliability of packaged integrated circuits by acting as an interposer between circuit and package components with large differences in their coefficients of thermal expansion, thus preventing die cracking and the like. In addition to having an appropriate modulus, and particularly important for packaging applications that include thermal cycling such as a lead-free soldering process, it is desirable for such a polymeric material to also have low internal stress and good thermal stability. However, heretofore known polymers can often be difficult to pattern as the etch properties of polymers and the photoresist compositions used for patterning them are very similar. Accordingly, efforts to selectively remove portions of the polymer can be problematic and it has been known to form an interposing material between the polymer and the resist composition where such interposing material can be selectively patterned and such patterned interposer material used for defining a pattern in the underlying polymer material.
The additional steps required to form a hard mask are generally not cost effective and hence alternate methods for patterning low dielectric constant polymer materials that do not require such steps would be advantageous. To this effect, U.S. Pat. No. 6,121,340 discloses a negative-working photodefinable polymer composition comprising a photoinitiator and a polycyclic addition polymer comprising repeating units with pendant hydrolyzable functionalities (e.g., silyl ethers). Upon exposure to a radiation source, the photoinitiator catalyzes the hydrolysis of the hydrolyzable groups to effect selective crosslinking in the polymer backbone to form a pattern. Thus the dielectric material of the '340 patent is in and of itself photodefinable. However, the polymer compositions disclosed in the '340 patent disadvantageously require the presence of moisture for the hydrolysis reaction to proceed. Since the presence of such moisture in the dielectric layer can lead to reliability problems in completed microelectronic devices and packages thereof, the materials of the '340 patent are usefully directed to other applications.
Recently, Japanese Patent No. JP3588498 B2, entitled “EPDXIDIZED CYCLOOLEFIN-BASED RESIN COMPOSITION AND INSULATING MATERIAL USING THE SAME” issued to Nippon Zeon, Ltd. (NZ patent). The patent is directed to providing a thin film excellent in heat resistance, solvent resistance, low water absorption properties, electrical insulating properties, adhesive properties, chemical resistance and the like. To this effect, the patent discloses various polymeric compositions where the polymer employed in the composition encompasses epoxy functional groups that can be crosslinked to provide a stable polymer film having the aforementioned properties. To obtain such a polymer encompassing epoxy groups, the NZ patent teaches first forming a polymer without epoxy functional groups and then subsequently grafting, by a free radical method, such groups to the polymer backbone, that is to say providing epoxy functional groups to one or more of the repeat units that form the polymer backbone. The patent teaches that such grafting requires an appropriate unsaturated epoxy group containing monomer and a free radical initiator, for forming a free radical on the backbone for the unsaturated monomer. While such a grafting reaction can successfully provide a polymer encompassing epoxy functional groups, the grafting will problematically lead to the addition (grafting) of epoxy groups at any of several positions within the repeat units and backbone as determined by the differences in reactivity of the different types of carbons present (the order of reactivity being primary<secondary<tertiary), as well as other factors such as the steric environment about each potential addition site and the number of sites available for addition. Thus some of the polymer's repeat units may have multiple epoxy functional groups grafted thereto, while other repeat units will have none. Furthermore, once an epoxy group containing monomer has been grafted, the functional group itself can offer sites for grafting making the composition of the resulting polymer unpredictable (See, Huang, et. al., “Fundamental Studies of Grafting Reactions in Free Radical Copolymerization” J. Polymer Science, Part A 33, 2533-2549 (1995)). Given this unpredictability, it should be obvious that it would also be problematic to graft more than one type of functional group onto the polymer backbone such that a specific desired result is obtained, or to create a polymer having selected functional groups at predetermined positions on the polymer backbone such that the resulting polymer is tailored to a specific use or application.
As the skilled artisan knows, a photodefinable polymer must have an essentially uniform composition so that an imagewise exposure of the polymer will have essentially the same effect on all portions of the polymer that are exposed. Given the compositional unpredictability of the NZ polymer composition, both among the plurality of polymer chains and within the plurality of repeat units of any one polymer chain, it is believed that the polymers and polymer compositions disclosed by the NZ patent, other than perhaps homopolymers and compositions thereof, are unlikely to be suitable as a photodefinable composition for microelectronic applications. Furthermore, it should also be realized that in addition to being unsuitable as a photodefinable polymer or polymer composition, the NZ polymers will have unpredictable physical and mechanical properties as a result of their unpredictable and hence non-uniform structural composition. Thus where it is beneficial to have a polymer with a low modulus of a specific range of values, the unpredictability of structural composition of the polymer that is formed by such a grafting reaction makes it unlikely that a specific range of modulus values can be obtained at all or if obtained, reproduced. Thus as it is advantageous to have a polymer that can be tailored to meet the specific requirements of an application, the NZ polymer and polymer compositions are at best problematic.
Therefore, it would be desirable to provide low dielectric constant polymeric materials having an appropriate modulus for use in the microelectronic and optoelectronic industries. It would further be desirable if such polymeric materials are in and of themselves photodefinable, do not require the presence of moisture to be photodefined and which can be tailored to have specific values physical, mechanical and chemical properties, for example modulus, internal stress and thermal stability. In addition it would be desirable to provide methods to make such photodefinable materials for a variety of appropriate uses, for example to form low dielectric constant films and microelectronic and/or optoelectronic devices that employ such films. It would also be desirable for the methods provided to allow the resulting polymer to be readily tailored to a specific use or application.